Semiconductor device and manufacturing method thereof

ABSTRACT

A semiconductor device includes: a resin substrate; a display element configured to generate an image; and a circuit layer including a thin film transistor configured to control the display element. The resin substrate has a main body made of resin and a surface layer made of the resin laminated on the main body. The surface layer has a lower electrification property than the main body or the surface layer has a lower film density than the main body. Each of the display element and the circuit layer is on the surface layer.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims priority from Japanese patent applicationJP2020-66472 filed on Apr. 2, 2020, the contents of which are herebyincorporated by reference into this application.

BACKGROUND 1. Field

The disclosure relates to a semiconductor device and a method ofmanufacturing the same.

2. Description of the Related Art

An organic electroluminescence display device has a light emitting layerconfigured to emit light in multiple gradations by passing a currentcorresponding to an input image signal, thereby displaying an image (JP2019-16504A). The current is controlled by a thin film transistor.

JP 2011-227369A discloses a flexible display including a flexible resinsubstrate on which a thin film transistor is formed. Such a resinsubstrate, with its easily chargeable surface, tends to affectcharacteristics of the thin film transistor.

SUMMARY

The disclosure aims at suppressing electrification property of a resinsubstrate.

A semiconductor device includes: a resin substrate; a display elementconfigured to generate an image; and a circuit layer including a thinfilm transistor configured to control the display element. The resinsubstrate has a main body made of resin and a surface layer made of theresin laminated on the main body. The surface layer has a lowerelectrification property than the main body or the surface layer has alower film density than the main body. Each of the display element andthe circuit layer is on the surface layer.

A method of manufacturing the semiconductor device includes: forming aresin substrate with a main body and a surface layer laminated on eachother, through application of a resin and baking the resin, the surfacelayer having a lower electrification property or a lower film densitythan the main body; forming a circuit layer including a thin filmtransistor on a surface of the surface layer of the resin substrate; andforming a display layer on the circuit layer, the display layerincluding a display element configured to generate an image.

This can suppress the electrification property of the resin substrate,because of the lower electrification property or the lower film density.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of a semiconductor device in a first embodiment.

FIG. 2 is a schematic view of the semiconductor device being used.

FIG. 3 is a III-III schematic cross-sectional view of the semiconductordevice in FIG. 2 .

FIG. 4 is a IV-IV cross-sectional view of the semiconductor device inFIG. 1 .

FIG. 5 is a detailed view of a resin substrate in the first embodiment.

FIG. 6 is a diagram of electrification characteristics of polyimide.

FIG. 7 is a diagram of a method of manufacturing a semiconductor devicein a second embodiment.

DETAILED DESCRIPTION

Hereinafter, some embodiments will be described with reference to thedrawings. Here, the invention can be embodied according to variousaspects within the scope of the invention without departing from thegist of the invention and is not construed as being limited to thecontent described in the embodiments exemplified below.

The drawings are further schematically illustrated in widths, thickness,shapes, and the like of units than actual forms to further clarifydescription in some cases but are merely examples and do not limitinterpretation of the invention. In the present specification and thedrawings, the same reference numerals are given to elements having thesame functions described in the previously described drawings and therepeated description will be omitted.

Further, in the detailed description, “on” or “under” in definition ofpositional relations of certain constituents and other constituentsincludes not only a case in which a constituent is located just on orjust under a certain constituent but also a case in which anotherconstituent is interposed between constituents unless otherwisementioned.

First Embodiment

FIG. 1 is a plan view of a semiconductor device in a first embodiment.The semiconductor device is actually bent and used. Therefore, FIG. 1 isa development view before the semiconductor device is bent. FIG. 2 is aschematic view of the semiconductor device being used. FIG. 3 is aIII-III schematic cross-sectional view of the semiconductor device inFIG. 2 .

The semiconductor device is, for example, an organic electroluminescencedisplay device. The semiconductor device has a display area DA in whichimages are displayed. In the display area DA, for example, a pluralityof unit pixels (sub-pixels) in some colors consisting of red, green, andblue are combined to form a full-color pixel, and a full-color image isdisplayed.

The semiconductor device includes a display 100. A spacer 102 isdisposed inside the bend to prevent the display 100 from being bent toomuch. The display 100 is flexible and folded outside the display area DA(in a peripheral area PA). A first flexible printed circuit board FP1 isconnected to the display 100 at the peripheral area PA. An integratedcircuit chip CP, for driving elements to display images, is mounted onthe first flexible printed circuit board FP1. Furthermore, a secondflexible printed circuit board FP2 is connected to the first flexibleprinted circuit board FP1.

FIG. 4 is a IV-IV cross-sectional view of the semiconductor device inFIG. 1 . The resin substrate 10 (array substrate) is made of polyimide.However, any other resin material may be used as long as it is a basematerial having sufficient flexibility for forming a sheet display or aflexible display.

On the resin substrate 10, a three-layer laminate structure of a siliconoxide film 12 a, a silicon nitride film 12 b, and a silicon oxide film12 c is provided as an undercoat layer 12. The lower most silicon oxidefilm 12 a is provided for improving adhesion with the resin substrate10, the middle silicon nitride film 12 b is provided as a blocking filmagainst moisture and impurities from the outside, and the uppermostsilicon oxide film 12 c is provided as a blocking film for preventinghydrogen atoms contained in the silicon nitride film 12 b from diffusingto a semiconductor layer 18 of a thin film transistor TR; the structureis not specifically limited thereto, may further include a laminate, ormay be a single layer or a double layer.

An additional film 16 may be formed under the undercoat layer 12 inaccordance with a portion where a thin film transistor TR is to beformed. The additional film 16 can suppress change in characteristics ofthe thin film transistor TR due to penetration of light from the backsurface of the channel, or can provide a predetermined potential bybeing formed from a conductive material to give a back gate effect tothe thin film transistor TR. Here, after the silicon oxide film 12 a isformed, the additional film 16 is formed in an island shape inaccordance with the place where the thin film transistor TR is formed,and then the silicon nitride film 12 b and the silicon oxide film 12 care laminated, so that the additional film 16 is sealed in the undercoatlayer 12; the structure is not limited thereto, the additional film 16may be formed first on the resin substrate 10, and then the undercoatlayer 12 may be formed.

The thin film transistor TR is formed on the undercoat layer 12. Apolysilicon thin film transistor is exemplified and only an N-channeltransistor is shown here but a P-channel transistor may be formed at thesame time. The semiconductor layer 18 of the thin film transistor TR hasa structure in which a low concentration impurity region is providedbetween a channel region and a source/drain region. A silicon oxide filmis used here as a gate insulating film 20. A gate electrode 22 is partof a first wiring layer W1 formed of molybdenum tungsten alloy. Thefirst wiring layer W1 includes a first holding capacitance line CL1 inaddition to the gate electrode 22. Between the first holding capacitanceline CL1 and the semiconductor layer 18 (source/drain region), via thegate insulating film 20, part of the holding capacitance Cs is formed.

On the gate electrode 22, the interlayer insulation film (silicon oxidefilm, silicon nitride film) is laminated. To easily bend the resinsubstrate 10, at least part of the interlayer insulation film 24 shouldbe removed in the folding area FA. The undercoat layer 12 is exposed byremoving the interlayer insulation film 24, at least part thereof isalso removed by patterning. After removing the undercoat layer 12, theresin material constituting the resin substrate 10 is exposed. In somecases, the surface of the resin material is partially eroded throughetching of the undercoat layer 12, resulting in film reduction.

On the interlayer insulation film 24, a second wiring layer W2 is formedto include portions serving as the source/drain electrode 26 and alead-out line 28. Here, it employs a three-layer laminated structure oftitanium, aluminum, and titanium. Through the interlayer insulation film24, the first holding capacitance line CL1 (part of the first wiringlayer W1) and the second holding capacitance line CL2 (part of thesecond wiring layer W2) constitute another part of the holdingcapacitance Cs. The lead-out line 28 extends to an end of the resinsubstrate 10 and has a terminal 30 to be connected to the first flexibleprinted circuit board FP1.

A planarization film 32 is provided to cover the source/drain electrode26 and the lead-out line 28 (except part of them). To form theplanarization film 32, organic materials such as photosensitive acrylicare often used because of superiority in surface flatness compared toinorganic insulating materials formed by chemical vapor deposition(CVD).

The planarization film 32 is removed at a pixel contact portion 34 andin the peripheral area PA, and a transparent conductive film 36 made of,for example, indium tin oxide (ITO) is formed thereon. The transparentconductive film 36 includes a first transparent conductive film 38 and asecond transparent conductive film 40 that are separated from eachother.

The second wiring layer W2, the surface of which is exposed by theremoval of the planarization film 32, is covered with the firsttransparent conductive film 38. A silicon nitride film 42 is provided onthe planarization film 32, covering the first transparent conductivefilm 38. The silicon nitride film 42 has an opening at the pixel contactportion 34; a pixel electrode 44 is laminated and electrically connectedto the source/drain electrode 26 through the opening. The pixelelectrode 44 is formed as a reflective electrode, and has a three-layerlaminated structure of an indium zinc oxide film, a silver film, and anindium zinc oxide film. Here, the indium zinc oxide film may be replacedwith a transparent conductive film. The pixel electrode 44 extendslaterally from the pixel contact portion 34, leading to above the thinfilm transistor TR.

The second transparent conductive film 40 is disposed adjacent to thepixel contact portion 34 and below the pixel electrode 44 (further belowthe silicon nitride film 42). The second transparent conductive film 40,the silicon nitride film 42, and the pixel electrode 44 are overlapped,thereby forming an additional capacitance Cd.

A third transparent conductive film 46 that is another part of thetransparent conductive film 36 is formed on a surface of the terminal30. The third transparent conductive film 46 is formed simultaneouslywith the first transparent conductive film 38 and the second transparentconductive film 40. The third transparent conductive film 46 on theterminal 30 is intended to be provided as a barrier film so that theexposed portion of the terminal 30 is not damaged in subsequentprocesses. During the patterning process of the pixel electrode 44, thethird transparent conductive film 46 is exposed to an etchingenvironment, but the transparent conductive film 36 is sufficiently maderesistant to the etching of the pixel electrode 44 by an annealingprocess performed during a period from the formation of the transparentconductive film 36 to the formation of the pixel electrode 44.

Above the planarization film 32, for example, above the pixel contactportion 34, an insulating layer 48, serving as a partition wall ofadjacent pixel regions and being called a bank (rib), is formed. To formthe insulating layer 48, photosensitive acrylic may be used like theplanarization film 32. The insulating layer 48 has an opening 58 toexpose the surface of the pixel electrode 44 for a light emittingregion; the opening 58 should have an end in a gently tapered shape.With the end of the opening 58 in a steep shape, the coverage of thefilm formed thereon is defective. The insulating layer 48 rests on aperiphery of each pixel electrode 44.

The planarization film 32 and the insulating layer 48 are in contactwith each other through an opening in the silicon nitride film 42between them. As a result, moisture and gas desorbed from theplanarization film 32 can be extracted through the insulating layer 48during heat treatment after the insulating layer 48 is formed.

An electroluminescent layer 50 made of an organic material is laminatedon the pixel electrode 44. The electroluminescent layer 50 also rests ona top surface of the insulating layer 48. A counter electrode 52 isprovided on the electroluminescent layer 50. Here, a top emissionstructure is employed; the counter electrode 52 is transparent. Forexample, a magnesium layer and a silver layer are formed so thin as totransmit light emitted from the electroluminescent layer 50. Accordingto the order of formation of the electroluminescent layer 50 describedabove, the pixel electrode 44 is an anode and the counter electrode 52is a cathode.

The counter electrode 52 is on the display area DA, extends to a cathodecontact portion 54 near the display area DA, is connected to the lowerlead-out line 28 at the cathode contact portion 54, and is electricallyconnected to the terminal 30.

A sealing film 56 is formed on the counter electrode 52. The sealingfilm 56 has a function of preventing external moisture from entering theelectroluminescent layer 50 that has formed, requiring a high gasbarrier property. Here, to form a laminated structure including asilicon nitride film, a silicon nitride film 56 a, a resin film 56 b,and a silicon nitride film 56 c are laminated. A silicon oxide film oran amorphous silicon layer may be provided between the silicon nitridefilms 56 a, 56 c and the resin film 56 b for improving adhesion.

If necessary, a cover glass or a touch panel substrate may be providedon the sealing film 56. In this case, a filler material using a resinmay be interposed to fill a gap between the sealing film 56 and thecover glass or the touch panel.

The semiconductor device includes a display element 60 (pixel electrode44, electroluminescent layer 50, counter electrode 52) for generatingimages. The semiconductor device has a circuit layer. The circuit layerincludes a thin film transistor TR for controlling the display element60.

FIG. 5 is a detailed view of the resin substrate in the firstembodiment. The resin substrate 10 includes a main body 64 made ofresin. The refractive index of the main body 64 is at least 3.08 and atmost 3.17. The filling rate of the main body 64 is at least 97 percentand at most 100 percent. The imidization rate of the main body 64 is atleast 99 percent and at most 100 percent.

The main body 64 is made of a polyimide comprising pyromelliticdianhydride (PMDA, also known as enzene-1,2,4,5-tetracarboxylicdianhydride). This is, for example, one in which PMDA and oxydianiline(ODA, also known as 3,4′-diaminodiphenyl ether) are repeatedly multiplebonded by an imide bond. Due to hardness compared to biphenyl andstretching characteristics similar to polyimide tape, the pyromelliticanhydride is extremely robust but has a high electrification property.

The resin substrate 10 includes a surface layer 62 made of resin. Thesurface layer 62 is laminated on the main body 64. The circuit layer isformed on a surface of the surface layer 62. The surface layer 62 has alower electrification property than the main body 64.

According to this embodiment, the surface layer 62 with the lowelectrification property can suppress the electrification in thevicinity of the interface between the resin substrate 10 and the circuitlayer. Specifically, the suppression of the electrification of thesurface layer 62 leads to suppression of the electrification of theundercoat layer 12 that is an insulating film such as SiN or SiOlaminated thereon, resulting in reduction of leakage current flowingbetween adjacent thin film transistors TR, through surface states formedas a result. Further, by suppressing the electrification of the surfacelayer 62, the occurrence of dielectric breakdown can be suppressed,whereby the occurrence of leakage paths from the thin film transistor TRto the resin substrate 10 is suppressed. Alternatively, by suppressingthe electrification of the surface layer 62, the shift of the thresholdvoltage of the thin film transistor TR is suppressed, thereby reducingan apparent current leakage.

The refractive index of the surface layer 62 is at least 3.00 and lessthan 3.08. The filling rate of the surface layer is at least 92 percentand less than 97 percent. The imidization rate of the surface layer 62is less than 99 percent. The surface layer 62 is made of polyimidecontaining diphenylene. The surface layer 62 has a poorer orientation inthe film thickness direction than the main body 64. The X-raydiffractive (XRD) strength ratio of the surface layer 62 to the mainbody 64 is 0.8 or less.

The inventor has found that, by forming the surface layer 62constituting the surface of the resin substrate 10 so as to have a lowfilling ratio and a low imidization ratio as described above, theelectrification property thereof can be suppressed more than that of theresin forming the main body 64. Here, as a result of the low fillingratio and the low imidization, the film density of the surface layer 62is lower than that of the main body 64.

The resin substrate 10 is formed by laminating the main body 64 and thesurface layer 62. The resin substrate 10 may be formed of an acrylicresin or an epoxy resin, instead of polyimide. The resin substrate 10 isformed through resin coating and resin baking. The resin substrate 10 isformed so that the surface layer 62 has a lower electrification propertythan the main body 64.

The processes of forming the resin substrate 10 include coating a resinfor forming the main body 64. For example, the resin is applied to aworking plate 66 such as a glass plate. Then, the resin for forming themain body 64 is baked. The baking is carried out by amplification ofmolecular motion (e.g., by infrared radiation) at a first temperature(e.g., 500° C.) Incidentally, the main body 64 has its lower surface(interface with the working plate 66), where molecules of the resin areuniformly oriented.

The processes of forming the resin substrate 10 include coating andbaking of a resin for forming the surface layer 62. The surface layer 62is formed to have a thickness of at most half (e.g., at most 20 percent)of the resin substrate 10. The resin for forming the surface layer 62 isbaked by applying hot air. By using the hot air, the solvent evaporatesnear the surface but hardly evaporates inside. Alternatively, the bakingis performed at a second temperature (e.g., 450° C.) lower than thefirst temperature. This can lower the electrification property of thesurface layer 62.

FIG. 6 is a diagram of electrification characteristics of polyimide. Thehorizontal axis indicates the wavelength of light irradiated to thepolyimide. The vertical axis indicates the photoluminescence intensity.At the light wavelengths of 400-500 nm, the photoluminescence intensitycorresponds to magnitude of charge, conductivity, and electrification.The photoluminescence intensity is higher in the order of the bakingtemperatures of 500° C., 450° C., and 400° C. That is, it is understoodthat the lower the baking temperature is, the lower the electrificationproperty becomes.

The circuit layer including the thin film transistor TR in FIG. 4 isformed on the surface of the surface layer 62 of the resin substrate 10.The display element 60 for generating images is formed over the circuitlayer. Finally, the semiconductor device is obtained by peeling theworking plate 66 in FIG. 5 .

Second Embodiment

FIG. 7 is a diagram for a method of manufacturing a semiconductor devicein a second embodiment.

In this embodiment, a resin is collectively applied as a material ofboth the main body 264 and the surface layer 262. Subsequently, duringthe baking of the resin, the main body 264 is heated, for example at500° C., by amplification of molecular motion of the main body 264(e.g., by infrared radiation). The infrared radiation can heat theobject from below. Then, the surface layer 262 is heated at a lowertemperature (e.g., 450° C.) than the main body 264, by transferring heatfrom the main body 264. Also in this embodiment, the electrificationproperty of the surface layer 262 is low, thereby suppressing theelectrification property of the resin substrate 210. With respect toother points, what is described in the first embodiment is applicable tothis embodiment.

The main body 264 and the surface layer 262 may be formed to have avertical relationship, by preparing and applying a base materialobtained by mixing different materials, and by utilizing layerseparation between the different materials until the applied resin layeris cured.

The embodiments described above are not limited and different variationsare possible. The structures explained in the embodiment may be replacedwith substantially the same structures and other structures that canachieve the same effect or the same objective.

Further, the present invention has the same effect in the manufacture ofa semiconductor device in which other display elements not limited toorganic EL elements and various functional elements not limited todisplay elements (specifically, e.g., light receiving element, detectionelement) are formed on a substrate made of resin.

What is claimed is:
 1. A semiconductor device comprising: a resinsubstrate; a display element configured to generate an image; and acircuit layer including a thin film transistor configured to control thedisplay element, wherein the resin substrate has a main body made ofresin and a surface layer made of the resin laminated on the main body,the surface layer has a lower electrification property than the mainbody or the surface layer has a lower film density than the main body,each of the display element and the circuit layer is on the surfacelayer, the main body is made of polyimide containing pyromelliticanhydride, and the surface layer is made of polyimide containingdiphenylene.
 2. The semiconductor device according to claim 1, whereinthe main body has a refractive index of at least 3.08 and at most 3.17,and the surface layer has a refractive index of at least 3.00 and lessthan 3.08.
 3. The semiconductor device according to claim 1, wherein themain body has a filling rate of at least 97 percent and at most 100percent, and the surface layer has a filling rate of at least 92 percentand less than 97 percent.
 4. The semiconductor device according to claim1, wherein the main body has an imidization rate of at least 99 percentand at most 100 percent, and the surface layer has an imidization rateof less than 99 percent.
 5. The semiconductor device according to claim1, wherein the main body has a greater orientation in a film thicknessdirection than the surface layer.
 6. The semiconductor device accordingto claim 1, wherein the surface layer has an X-ray diffraction intensityratio of 0.8 or less to the main body.
 7. The semiconductor deviceaccording to claim 1, wherein the resin substrate has molecules of theresin in a uniform orientation on a surface opposite to the surfacelayer.
 8. The semiconductor device according to claim 1, wherein thesurface layer is at most half as large in film thickness as the resinsubstrate.
 9. A method of manufacturing the semiconductor device, themethod comprising: forming a resin substrate with a main body and asurface layer laminated on each other, through applying and baking aresin, the surface layer having a lower electrification property or alower film density than the main body; forming a circuit layer includinga thin film transistor on a surface of the surface layer of the resinsubstrate; and forming a display layer on the circuit layer, the displaylayer including a display element configured to generate an image,wherein the main body is formed of polyimide containing pyromelliticanhydride, and the surface layer is formed of polyimide containingdiphenylene.
 10. The method of manufacturing the semiconductor deviceaccording to claim 9, wherein in the step of forming the resinsubstrate, applying and baking a portion of the resin for forming themain body and applying and baking another portion of the resin forforming the surface layer are separately carried out.
 11. The method ofmanufacturing the semiconductor device according to claim 9, wherein aportion of the resin for forming the main body is baked by amplificationof molecular motion, and another portion of the resin for forming thesurface layer is baked by applying hot air.
 12. The method ofmanufacturing the semiconductor device according to claim 9, wherein aportion of the resin for forming the main body is baked at a firsttemperature, and another portion of the resin for forming the surfacelayer is baked at a second temperature lower than the first temperature.13. The method of manufacturing the semiconductor device according toclaim 9, wherein the surface layer is formed to be at most half as largein film thickness as the resin substrate.
 14. The method ofmanufacturing the semiconductor device according to claim 12, whereinthe surface layer is formed to be at most 20 percent as large in filmthickness as the resin substrate.
 15. The method of manufacturing thesemiconductor device according to claim 9, wherein in the step ofapplying the resin, the resin is collectively applied as a material ofboth the main body and the surface layer, and in the step of baking theresin, the main body is heated by amplifying molecular motion of themain body, and heat is transferred from the main body to the surfacelayer, thereby heating the surface layer at a lower temperature than themain body.